The field of the invention is engine generator sets, and particularly, small compact generator units for portable use or for use in recreational vehicles.
Small, vertical shaft engine generator sets such as those disclosed in U.S. Pat. Nos. 4,450,888 and 4,677,940 include a small gasoline or gas powered engine which rotates the rotor of an electric generator. Heat is produced by both the engine and generator and this heat must be removed for proper system operation. Portable generators are housed in a compact, aesthetically pleasing enclosure, and generators for recreational vehicles are housed in compact compartments formed in the vehicle. In both applications the proper removal of heat is a significant design challenge.
The conventional solution for removal of heat is to provide separate cooling fans for the engine and the generator. As disclosed in the above-cited patents, for example, a fan is disposed on top of the engine and is driven by the vertical engine shaft to blow cooling air over the air-cooled engine. The generator is mounted below the engine, and the generator rotor and a generator cooling fan are both driven by the vertical engine shaft. The generator cooling fan cools the generator stator windings and it may also provide some engine cooling as well. The use of two fans in systems such as these is expensive, and the use of two fans increases the vertical height of the generator set.
A vertical shaft, engine generator set which employs a single cooling fan is disclosed in U.S. Pat. Nos. 4,779,905 and 4,856,470. In these systems cooling air is drawn in over the engine and then around the generator stator windings before being exhausted. Because the engine is cooled first, proper cooling of the more sensitive generator windings is problematic, particularly when a more compact generator construction is used. Also, there is no provision for cooling electronic circuitry which is used on state-of-the-art generator sets to regulate generator output voltage.